The present invention relates generally to milling machines, and more particularly to a rigid tapping feedback assembly that is adapted for retrofitted use on conventional milling machine to determine a rate of revolution of a spindle.
Milling machines, such as a knee mill, turret mill, or vertical mill, are common in the fabrication industry. Typically, milling machines include a spindle, an endmill or cutter tool that is attached to, and rotates concurrently with, the spindle. The spindle can be extended along the generally vertically orientated spindle axis, e.g., Z-axis, allowing for plunge cuts and drilling of a work piece. The work piece is affixed to a table that is located below the endmill and is typically moveable in the X-axis and Y-axis.
During operation, the spindle may be manually lowered along the Z-axis (e.g., generally vertically), or automatically adjusted by a computer numerical control (CNC) controller. The CNC controller sends a signal to an automated drive (e.g., carried out by a stepper or servo motors) that extends the spindle according to a predetermined feed rate. For particular automated drives, feedback of the position of the spindle is transmitted to the CNC controller such that the position of the spindle, or quill, can be continuously monitored. Accordingly, the depth of the cut in the z-direction is held constant and the cutting operation is repeatable between a plurality of work pieces.
Typically, the predetermined feed rate is established based upon the pitch of the tap to be machined and the rotational speed of the spindle as set on the milling machine motor. But, if the spindle rotates at a speed other than the set rotational speed, the predetermined feed rate of the spindle will be unaffected and cause the CNC controller to drive the spindle downward causing undue stress on the tool. As such, the present invention pertains to a rigid tapping feedback assembly that may be retrofitted onto a conventional milling machine. Significantly, the design of the rigid tapping feedback assembly provides additional input to the CNC controller that controls the operation of the automated drive.